President Trump hit back at Republican Sen.-elect Mitt Romney of Utah for his criticisms Wednesday, saying he hopes Mr. Romney isn’t a new “Flake” who will be attacking the president within the GOP.

“Here we go with Mitt Romney, but so fast!” Mr. Trump tweeted. “Question will be, is he a Flake? I hope not.”

It was a reference to retiring Republican Sen. Jeff Flake of Arizona, who has often criticized Mr. Trump’s actions and hasn’t ruled out a primary challenge against the president in 2020.

In an op-ed in The Washington Post, the newly elected Mr. Romney said Mr. Trump “has not risen to the mantle of the office.” He said the president has gone into a “deep descent” in the past month.

Mr. Trump said he would “much prefer that Mitt focus on Border Security and so many other things where he can be helpful.”

“I won big, and he didn’t. He should be happy for all Republicans. Be a TEAM player WIN!” the president tweeted, apparently referring to Mr. Romney’s loss in the presidential election of 2012 to President Barack Obama.

Trump campaign manager Brad Parscale said the truth is that Mr. Romney “lacked the ability to save this nation,” while Mr. Trump “has saved it.”

“Jealously is a drink best served warm and Romney just proved it. So sad, I wish everyone had the courage @realDonaldTrump had,” Mr. Parscale tweeted.